1. Field of the Invention
This invention relates to systems which are used to periodically measure the distance between fixed points on two or more objects which are constrained to move relative to each other. More specifically, this invention relates to a measuring device based on the Wiedemann effect which is capable of measuring longer distances, is less expensive to manufacture and which offers improved performance relative to previous systems of this type.
2. Description of the Prior Art
In modern machine tools, elevators and other mechanical systems, it is often essential to accurately and frequently measure distances between points on certain relatively movable system components. In an elevator system, for example, the position of the elevator relative to the respective floors needs to be precisely monitored and updated while the elevator is operating. In a machine tool system, the position of the tool relative to the workpiece likewise needs to be precisely and continuously monitored.
One system which has enjoyed a great deal of commercial success in applications which require relatively small distances to be monitored is the TEMPOSONICS.TM. system that is described in U.S. Pat. No. 3,898,555 to Tellerman. The TEMPOSONICS.TM. system is manufactured and marketed by the assignee of this application, MTS Systems Corporation of Minneapolis, Minnesota.
The TEMPOSONICS.TM. system relies upon a permanent magnet which is mounted to one body, and a transducer which is mounted on a second body that is constrained to move relative to the first body. To measure the distance between the bodies, the transducer generates a signal, and receives a return pulse that is created at the location of the permanent magnet by the Wiedemann effect. The system measures the elapsed time between the pulses, and thus calculates the relative distance between the two bodies.
While the TEMPOSONICS.TM. system has proven successful in short distance measurement applications, it has inherent technical limitations that prevent it from measuring distances greater than about five meters with its characteristic degree of resolution. Such systems, however, have inherent advantages over other distant measurement techniques. It is clear that a long and unfilled need has existed in the prior art for a Wiedemann effect type distance measurement system which is capable of measuring longer distances than those systems which have heretofore been known.